Evaluation of Shortwave Irradiance and Evapotranspiration Derived from Moderate Resolution Imaging Spectroradiometer (MODIS)

초록

In this study, the modified RS-PM model (Mu et al., 2007) was revised to estimate land surface evapotranspiration (ET) by using MODIS products only. Our stand alone algorithm was devised to utilize MODIS atmospheric and land products to estimate input variables for the PM model including net radiation, vapor pressure, and canopy conductance. Also, a simple gap filling approach was proposed for the MODIS aerosol data that was identified as a bottleneck to determine retrieval rates of global radiation and ET. Ground global radiation data from 22 National Weather Stations (NWS) from 2004 to 2006 were utilized to test and improve MODIS global radiation and the gap filling algorithm. Evapotranspiration observed at two KoFlux sites were analyzed to assess the accuracy of MODIS ET. The retrieval rate of MODIS global radiation was doubled up to 42 and 44% for Terra and Aqua, respectively, after the aerosol gap filling with negligible compromise of the accuracy. In spite of the high accuracy of MODIS driven input variables (i.e. global radiation and net radiation), MODIS ET showed meaningful errors at the two KoFlux sites. MODIS ET for partial clear sky condition showed almost similar errors to those for clear sky condition, while retrieval rates were increased nearly twofold. Our study indicates that more endeavors are necessary on improving the accuracy and the model needs to be tested across many geographic locations with different climate regimes, biome types, and landscape complexity.

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